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The 'worldwide web' of forest pathogens

Bernard Slippers: Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria

<div>Despite the development of increasingly strict biosecurity measures during the course of the past two decades, the rate at which tree-associated fungi are moving globally continues to increase. Population genetics studies show that many of these pathogens have globally distributed genotypes and that they establish seemingly unstructured global meta-populations. These population genetics patterns can be explained only by introductions of large numbers of genotypes or multiple introductions over time. The apparent scale and frequency of these introductions could also fast track the evolution of pathogens through hybridization and admixture that might lead to unique adaptations. The diversity in this growing global pool of invasive pathogens increases their potential to overcome host resistance and environmental variation that usually restricts population growth of pathogens, and likely contributes to increasingly frequent and serious outbreaks. We have undertaken a meta-analysis of population genetics and phylogeographic studies of selected globally distributed forest pathogens in an attempt to visualize what we view as a 'worldwide web' of forest pathogens. Furthermore, we elucidate mechanisms that facilitate the movement and establishment of these pathogens. Based on these insights, we also consider the manner in which an apparent constant flow of introductions might be slowed down.</div>

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